The lithium, thionyl chloride battery is one of the most powerful batteries known. The power of the lithium, thionyl chloride battery is in the order of 25 times as much as the common lead acid type battery. The lithium, thionyl chloride battery is desired for many low rate applications such as heart pacemakers, fire alarms, watches, and calculators. The U.S. Navy has been experimenting with lithium, thionyl chloride batteries for higher rate applications, such as powering torpedoes. In order to power a torpedo a number of the lithium, thionyl chloride batteries are connected in series. A serious drawback to the lithium, thionyl chloride battery is its potential for exploding like an incendiary bomb when shorted out or subjected to a reverse voltage. In a reverse voltage condition the lithium in the battery tends to electroplate a very thin wirelike structure or dendrite between the anode of lithium and cathode current collector. In the reverse voltage condition the dendrite will flash or burn up and, if there is the presence of elemental sulfur, the incendiary type explosion takes place. Much effort has been expended by many researchers to resolve this explosion problem of the lithium, thionyl chloride battery.
A situation where the lithium, thionyl chloride battery is particularly susceptible to explosion is where it is connected in series with a number of other lithium, thionyl chloride batteries. If one of these batteries in the battery string is of less capacity, weaker, or partially used after originally being of the same strength as the other batteries, a reverse voltage condition will ensue when the battery has reached the end of its capacity. This depleted battery in the string of batteries will then undergo a reverse voltage condition and will be immediately susceptible to violent explosion due to the growth of lithium dendrites. The hoped for situation is that only batteries of the same capacity are connected in series. However, because of human error it is possible that one of the batteries in a string of batteries is of a lesser capacity than the other batteries in the string. It is this dangerous situation which is overcome by the present invention.